Adds a 3x entry to the export scale selector in the workspace design
sidebar and in the viewer inspect panel, so @3x assets can be exported
natively without resizing them in external tools.
Signed-off-by: Shreyash Agare <agareshreyash26@gmail.com>
Co-authored-by: Shreyash Agare <agareshreyash26@gmail.com>
Co-authored-by: Andrey Antukh <niwi@niwi.nz>